He worked at top secret Canadian naval military facilities and had clearance to intelligence-sharing systems linked to countries such as the US and UK.

For nearly four years he copied secret information onto memory sticks to share with his handlers in Moscow.

He apparently walked into the Russian embassy in Ottawa in 2007 to volunteer his services, and was arrested in January.

Communism not cash

The case has resulted in severe and irreparable damage to Canada's relationship with its allies, a Nova Scotia provincial court heard on Wednesday.

the BBC's Lee Carter in Toronto says the 41-year-old's guilty plea came as a surprise. It means a publication ban has been lifted allowing details from the case to be published for the first time.

At a bail hearing in March, portions of a police statement were read out in which he reportedly described the day he walked into the embassy as "professional suicide".

"The day I flipped sides... from that day on, that was the end of my days as Jeff Delisle," said the statement.

He is expected to be sentenced in January and could face anything from five years to life in prison.

Suspicions were raised when Delisle returned in 2011 from a four-day trip to Brazil - where he had met a Russian handler - with several thousands dollars in cash.

That prompted the involvement of the Royal Canadian Mounted Police, who broke into an email account he shared with his handlers.

He is the first Canadian to be convicted under the country's Security of Information Act, passed by parliament after the 11 September attacks on the US.

Delisle joined the navy as a reservist in 1996, became a member of the regular forces in 2001 and was promoted to an officer rank in 2008.

He reportedly worked for a unit that tracked vessels entering and exiting Canadian waters, with access to information shared by the Five Eyes community that includes Canada, the United States, Britain, Australia and New Zealand.

Canada's military has not revealed any details about any information disclosed to the Russians.

Mike Taylor, for the defence, said his client had never put any Canadian troops in danger.

"There was no information that indicated where troops were or ships were," he told the Associated Press news agency.